、。
She reversed her decision again, which infuriated all of us.
Literal
[topic-は] again decision [object-を] overturned, that thing-は we everyone [object-を] caused-anger.
覆す ('overturn, reverse, refute') is a Sino-Japanese-flavored verb covering legal verdicts (判決を覆す), policies, decisions, theories — anything that can be flipped from one stance to its opposite. 決心 ('resolution, made-up mind') is a slightly elevated noun for the decision itself. The second clause uses そのことは ('that matter') to refer back to the entire reversal — a typical Japanese way of nominalizing an event for further comment. 怒らせる ('cause to be angry') is the causative of 怒る ('be angry'), with the experiencer marked by を — みんなを怒らせる ('infuriated everyone'). The また ('again') flags this as a recurring pattern, sharpening the irritation.